The invention lies in the field of vacuum electronics and is to be used in the gas-tight soldering of a ceramic component to a copper component using a soldering material.
The production of gas-tight soldered joints between a ceramic component and a copper component is conventional, for example, in high-power tubes and vacuum switching tubes. For vacuum switching tubes, a soldering technique is known in which a cupped copper casing is butt soldered to a ceramic sheet, i.e., in which so-called cut soldering is performed. Here, the ceramic sheet is first metal-plated in the area where the soldered joint is to be placed. To produce the soldered joint, a soldering ring is put down in the transition area between the copper component and the ceramic component, which soldering ring melts during the heat treatment required for soldering, the soldering material joining the copper component and the ceramic component to one another in the area of their boundary surfaces (EP 0 040 933 B1, FIGS. 7 and 8). Here, it is conventional to use as the soldering material so-called copper-silver-eutectic solders which come in the form of a film or a wire ring (xe2x80x9cHandbuch der Vakuumelektronikxe2x80x9d [Handbook of Vacuum Electronics], Josef Eichmeier and Hinrich Heynisch, R. Oldenbourg-Verlag Mxc3xcnchen/Wien, 1989, p. 22).
To produce a soldered joint between a ceramic component and a metallic component, e.g., to produce a gas-tight and adherent soldered joint in the production of a vacuum switching tube, a soldering technique is known in which a first layer made of silver and then a further layer made of copper are applied to the ceramic component following its metallization in the area where the soldered joint is to be placed. Following the connection of the components to be joined, a homogeneous copper/silver alloy forms under the soldering conditions which constitutes the actual soldering means. Moreover, especially for soldering a ceramic component to a copper sheet, it is provided to deposit silver alone on the metal-plated ceramic component using electroplating technology. When the components to be joined are heated to 961xc2x0 C., an eutectic having a melting point of about 780xc2x0 C. then forms in the area of the copper sheet (DE 38 24 900 A1). This soldering technique, in which in other words the surface layer of the copper component in the area of the connection point is drawn upon to form the actual solder, appears suitable only for butt soldered joints but not for cut soldered joints.
Starting with a process having the features of the generic part of patent claim 1 (DE 38 24 900 A1), the underlying object of the invention is to simplify and to improve the production of such a soldered joint by making available a larger quantity of soldering means.
To meet this objective, it is provided according to the invention that the copper component is provided galvanically with a silver layer in the area where the soldered joint is to be placed as well as in surface areas bordering the actual location where the soldered joint is to be placed prior to the heat treatment.
In a process of this sort, it is unnecessary to carry out a very often difficult alignment of the soldering material to the soldering location. By incorporating a larger surface layer of the copper component as a constituent of an eutectic alloy which does not arise until the soldering process, the handling of the soldering process, including the galvanic application of the silver layer, whose thickness can lie in the range from 2 to 100 xcexc depending on the soldering surface and the geometry of the copper component, is significantly simplified. Particularly with cut soldered joints, a sufficiently large quantity of soldering material is made available in this manner. In special application cases, it is thus possible to use the soldering process for joining the copper component to the ceramic component simultaneously for producing further soldered joints, in particular for joining the copper component to other metal components. In these cases, the copper component as a whole can have a silver layer. For example, in the production of vacuum switching tubes, i.e., of components having a vacuum-tight casing, the copper component, assuming it forms a casing cap or a casing flange, can be simultaneously soldered to the bellows and to a bearing seat for the introduction of the movable contact stud.